Internal recirculation burner

ABSTRACT

An air-fuel combustor having a swirl inducing device at the inlet end thereof for producing premixing of air and fuel in a mixing chamber upstream of a combustion chamber and to produce a reverse recirculation of combustion gases from a downstream combustion chamber through the mixing chamber. An inner deflector plate forming the combustion chamber has an annular deflector plate forming the combustion chamber has an annular nozzle supported thereon which is supplied with primary air to produce an attached wall jet flowing across the inner deflector plate of the combustion chamber to promote recirculation flow therethrough and to promote reversal of flow of the recirculation pattern at one end of the combustion chamber to reduce pressure drop through the combustor assembly.

United States atent 1191 Quinn 1 Dec. 3, 1974 [73] Assignee: General Motors Corporation,

Detroit, Mich.

[22] Filed: Nov. 5, 1973 [21] Appl. No.: 412,661

France.... 431/116 Primary Examiner-Edward G. Favors Attorney, Agent, or Firm-J. C. Evans [5 7] ABSTRACT An air-fuel combustor having a swirl inducing device at the inlet end thereof for producing premixing of air and fuel in a mixing chamber upstream of a combustion chamber and to produce a reverse recirculation of combustion gases from a downstream combustion chamber through the mixing chamber. An inner deflector plate forming the combustion chamber has an annular deflector plate forming the combustion chamber has an annular nozzle supported thereon which is supplied with primary air to produce an attached wall jet flowing across the inner deflector plate of the combustion chamber to promote recirculation flow therethrough and to promote reversal of flow of the recirculation pattern at one end of the combustion chamber to reduce pressure drop through the combustor assembly.

5 Claims, 8 Drawing Figures INTERNAL RECIRCULATION BURNER This invention relates to fuel and air combustor as-. semblies and more particularly to combustors including means therein for promoting recirculation of combustion gases to heat inlet and air-fuel mixtures prior to passage thereof into the inlet end of a primary combustion zone.

Various combustor designs have been proposed and tested using either swirl or jet induced recirculation for mixing the heated combustion products with the fresh fuel-air mixture. Particularly, pumping by an attached wall jet or Coanda jet has been usedto obtain a high ratio'of recirculated products to primary combustion air flow. In the attached jet type recirculation combustor it is usually necessary to employ a separate means for flame stabilization such as a flow dividing orifice. However, by use of the present invention it has been demonstrated that the recirculation flow induced by swirl can support stable combustion without the necessity for a separate flame holder.

In the subject invention it is proposed that a combustor design employ both attached jet and swirl effects operating in conjunction to produce recirculation with performance which is superior to designs in which either of these effects are used separately to cause recirculation. Specifically, combustor assemblies employing only swirl effects to induce recirculation have demonstrated smaller quantities of recirculation than equivalent designs employing attached jet pumping. On the other hand, the attached jet types employ flame holders which increase system pressure loss and limit recirculation.

An object of the present invention is to combine the actions of jet pumping and swirl effects in a combustor assembly to produce an improved recirculation flow pattern therein for inducing recirculation through a primary combustion zone, into a premixing chamber for prevaporization of fuel particles prior to passage into the primary combustion chamber to reduce emissions from the combustor and to reduce pressure loss across the assembly.

Another object of the present invention is to improve the blow out characteristics of a combustor assembly operating under lean fuel-air ratios by the provision of a swirl producing means directing primary air into a mixing chamber along with fuel with the swirl device producing a recirculation pattern through a primary combustion chamber into the mixing chamber to increase prevaporization of fuel in the mixing chamber and by the further provision of jet pumping means directing a second portion of primary air with respect to the recirculating pattern produced by the swirl means to increase the quantity of recirculation between the primary combustion chamber and the mixing chamber to increase prevaporization therein.

Still another object of the present invention is to improve the operation of a combustor assembly of the type having an outer casing defining a premixing entrance chamber and including .a combustor liner located in spaced relationship to the outer casing to define an annular recirculation chamber therebetween and wherein swirl means are provided to produce a recirculation pattern through a combustion chamber within the liner and the annular chamber for heating the air-fuel mixture in the mixing chamber to produce pump means for directing primary air with respect to the swirl induced recirculating flow through the combustion chamber to increase the rate of recirculation so as to improve the blow out characteristics of the combustor assembly when operating under lean air-fuel ratio conditions.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein a preferred embodiment of the present invention is clearly shown.

In the Drawings:

FIG. 1 is a view in vertical cross section of a combustor assembly including the present invention;

FIG. 2 is an end elevational view looking in the direction of the arrows 2-2 in FIG. 1:

FIG. 3 is an enlarged, fragmentary sectional view of a nozzle lip in the assembly of FIG. 1;

FIG. 4 is a sectional view taken along the line 4-4 of FIG. 1 looking in the direction of the arrows;

FIG. 5 is a longitudinal cross sectional view of a second embodiment of the invention;

FIG. 6 is an end elevational view taken along the line 6-6 of FIG. 5 looking in the direction of the arrows;

FIG. 7 is a cross sectional view taken along the line 7-7 of FIG. 6; and

FIG. 8 is an enlarged fragmentary vertical sectional view taken along the line 8-8 of FIG. 5 looking in the direction of the arrows.

Referring now to FIG. 1, a combustor assembly 10 is illustrated having an outer casing 12 with an inlet end 14 andan outlet tube 16 on the opposite end thereof. The outlet end 16 is joined to the outer diameter of the outer casing 12 by an annular section defining a curved reentrant surface 18 around the inner end 20 of the outlet tube 16.

A swirl plate 22 is located in the inlet end 14 of the outer casing 12. It includes a central opening 24 therethrough in which is supported a fuel nozzle assembly 26. Fuel nozzle 26 more particularly includes a bushing 28 welded at one end thereof to the outer surface of the plate 22 around the opening 24 therein. An elongated nozzle tube 30 is supportingly received by the bushing 28 and is directed from exteriorly of the plate 22 into the interior of the outer casing 12. The tube 30 has an internally threaded fuel nozzle adapter 32 secured on one end thereof into which a fuel distributing nozzle 34 is threadably received.

Additionally, the nozzle tube 30 has a tube transition adapter 36 located therein that supportingly receives the open end of a fuel supply tube 38 that is directed from that point exteriorly of the nozzle tube-30 for connection to a suitable fuel supply source.

A combustion chamber liner 40 of increasing diameter from end-to-end thereof is located within the outer casing 12 in spaced relationship with the inner surface thereof to define an annular external recirculation flow passage 42 therebetween. The combustion liner 40 is supported in its spaced relationship by six equally circumferentially spaced ducts 44 each connected at an outer opened end 46 thereon to the outer surface of the casing 12 around a primary air inlet opening 48 therein.

- from the inlet end of the combustion liner toward the longitudinal axis thereof to a reduced diameter at 60 defining a diffuser section 62 at one end of a primary combustion zone 64 within the inner deflector plate 54. From the reduced diameter 60 thereof the deflector plate 54 includes a plurality of transition surfaces 66, 68, 70, 72 each being directed at a greater outwardly diverging angle with respect to the longitudinal axis of the combustion chamber liner 40 from the reduced diameter 60 of the plate to a maximum outer radial diameter 74 thereon.

An annular nozzle lip 76 has one end 78 thereon welded to a large diameter end 80 of the combustion liner 40. It further includes a curved outer surface 82 thereon cooperating with the curved reentrant surface 18 to form a return path 84 from the annular passage 42 into the outlet end of the primary combustion zone 64.

By virtue of the provision of a large diameter outlet end 80 of the combustion liner 40, the annular passage 42 between the combustion liner 40 and the outer casing 12 has a decreasing cross sectional flow area from an inlet end 86 thereon to an outlet end 88 thereon which merges with the return path 84 thereby to produce increased velocity of recirculation flow from an inlet mixing chamber 90 formed within the outer casing upstream of the primary combustion zone 64 formed within the combustion liner 40 and the deflector plate 54.

Primary air flow into the mixing chamber 90 is through a plurality of swirler vanes 91 defining equally spaced grooves 92 formed in the outer periphery of the plate 22 at circumferentially spaced points therearound. Each of the grooves, as best seen in H0. 3 is formed at an angle with respect to the axis of the plate 22 so as to produce a swirl pattern of primary air flow into the chamber 90 which will mix with fuel distributed from the nozzle 34 prior to passage into the primary combustion zone 64.

The swirl pattern produced by the grooves 92 includes a component of velocity tangential to the inner surface of end 14. It will be directed through the annular passage 42 from the inlet 86 to the outlet 88 thereof thence through the return path to produce a reverse axial recirculation through the primary combustion zone 64 from an outlet end 94 thereof to the inlet end 96 thereof. A second quantity of primary air is directed through the ducts 44 into a plenum 98 formed between the deflector plate 54 and the combustion liner 40. The primary air is then discharged through an'annular gap 100 formed between the maximum radially outer diameter 74 on the plate 54 and the inner annular edge 102 of the nozzle lip 76 to produce a jet stream that adheres to the transition surfaces 68 through 72 at a point radially outwardly of the reverse axial recirculation flow produced by the swirl grooves 92 at the opposite end of the combustor assembly.

Thus, the primary or fresh air enters the system at the grooves 92 to produce a general pattern of axial recirculation flow from the mixing chamber 90 and the annular chamber 42 where the flow reverses to produce a reverse axial recirculation flow through the combustion chamber. The remainder of the primary air which enters a combustor assembly 10 through the ducts 44 into the plenum 98 for discharge through the gap 100 produces an internal Coanda jet flow across the transition surfaces which adheres thereto. The swirl component recirculation represents a driving force to increase the rate of recirculation over combustors having a jet flow pattern alone. Furthermore, the jet produced by the nozzle gap 100 and the adhering flow thereof across the transition surfaces results in a relatively cool nonswirling driving force that surrounds relatively hot swirling recirculation gas which is directed through the core of the combustion chamber. This tends to promote mixing between the two streams at their interface with a resultant entrainment which produces an improved rate of recirculation flow through the combustion chamber. This recirculation flow which is heated by combustion within the combustion chamber 64 enters the mixing chamber where it swirls with respect to the fuel droplets directed from the nozzle 34 to be intimately mixed therewith to produce prevaporization of the fuel supply before it enters the combustion chamber. Within the combustion chamber, the prevaporized and mixed air-fuel components produce a stable combustion process. By virtue of the pattern described above and the premix, prevaporization of the air fuel within the mixing chamber 90 relatively lean air-fuel ratios can be introduced into the combustion chamber without undesirable blow out of the combustion process at zone 64.

In combustion devices of the type having swirl induced recirculation paths therethrough pressure losses which tend to limit the quantity of recirculation flow are associated with a 180 change of flow at both axial ends of an external recirculation flow path. In the present invention, however, pump means are intimately associated with each of the turning processes, namely, the swirl grooves 92 at one end of the recirculation path and the jet producing gap at the opposite end thereof. It is known that losses associated with an accelerating flow process such as a nozzle tend to be lower than with a decelerating or stagnating flow process such as a diffuser. Dividing the flow pumping or accelerating actions in the present invention between the two ends of the combustion chamber 64 will materially reduce the overall pressure loss otherwise resisting recirculation flow through the combustion chamber for use in prevaporization of fuel supply to the combustor assembly 10. Thus, by virtue of the aforedescribed arrangement, a given quantity of recirculation is obtained at a lower overall combustorpressure loss.

A further advantage of the aforedescribed arrangement is that it is not absolutely necessary to introduce separate dilution air at a downstream location as is common practice in air-fuel combustor apparatus. The relative stability of a layer of swirling primary air adhering to the inner wall of the combustion chamber as produced by the Coanda nozzle effect will be delayed to a position relatively downstream of the primary combustion zone 64 to serve this purpose.

A further feature of the invention is that the gap of the Coanda nozzle is at a central location with the combustion chamber. This location is preferred over an arrangement wherein the gap is on the external portion of the inner deflection surface. Such an arrangement would cause a diffusion section downstream of the jet mixing section to have a higher wetted perimeter per unit of cross sectional area than for an internal diffusing section as illustrated in the present invention. As shown, the confinement of the high velocity portions of the recirculation flow path to the internal portion of the combustion chamber tends to reduce viscous losses over a system where the jet is located externally thereof.

Another inherent advantage of the internal jet location is that the jet flows into a region of decreasing available area from the maximum diameter location 74 to the reduced diameter portion 60 of the internal deflector' plate 54 in a direction normal to flow. This results in a reduced tendency for jet separation and/or reversal of the direction of the entrained flow velocity.

A further advantage of the arrangement in the present invention is that in systems that employ recirculation induced by swirl components only, there is a secondary recirculation between the combustion zone products and the incoming swirling primary air. This is distinct from the recirculation due to reversal of the axial velocity of the central vortex in swirl recirculation systems. This secondary recirculation is associated, in cases of combustion with swirl only, with mixing around the peripheral boundary between the primary swirling flow and the fuel-air mixing zone. This secondary mixing can account for some of the undesirable features with respect to exhaust emissions found in combustor designs depending solely on swirl effects to induce recirculation. In the present arrangement, there is a better control over this secondary recirculation effect because of the attached wall jet produced by the gap 100 as directed across the inner surface of the deflector 54. By optimization of the additional geometric variable defined by the surface of the deflector 54 and the location of the jet gap, it is possible to confine the secondary recirculations to regions outside the fuel-air mixing zone.

FIGS. 5 through 8 illustrate a second embodiment of the invention including a combustor assembly 104 having an outer casing 106 with an outlet tube portion 108 thereon and a curved inlet dome 110. A central opening 112 in the inlet dome lsupportingly receives a swirler tube 114 which is welded thereto at 116.

The swirler tube 114 has an opened entrance end 118 thereon for supply of primary air through a swirler assembly 120 whichincludes a center body 122 having a large diameter inlet end 124. End 124 is spaced with respect to the inner surface of the swirler tube 114 at the opened end 118 thereof. Body 122 has a decreasing diameter to define a nose portion 126 terminated centrally of an outlet end 128 of the tube 114. The swirler center body 122 is connected to the inner surface of the swirler tube 114 adjacent the open end 118 thereof by a plurality of swirler vanes 130 which are located at circumferentially spaced points along the periphery of the inlet end 124. Each of the swirler blades has a root portion 132 thereof connected to the center body 122 and a tip portion 134 thereof fixed to the inner surface of the tube 114 at the open end 118.

As best seen in FIG. 7, each of the swirl vanes has a passage 136 formed therebetween which is directed at an angle with respect to the axis of the center body 122 to produce a clockwise swirl as viewed from the swirler end of the liner, elevational view in FIG. 6.

Fuel is directed into the interior 138 of the swirler tube downstream of the swirler vanes 130 by an annular channel supply conduit 140 that has the edges thereof welded to the outer surface of the swirler tube 1 14 in overlying relationship with a plurality of circumferentially located fuel supply openings 142 in the tube 114. A fuel supply conduit 144 is connected to the annular conduit for directing fuel into the interior 138 through the holes 142 downstream of the swirler vanes 130 to produce premixing of the fuel and primary air therein. The mixed air-fuel passes into a prevaporization mixing chamber 146 that is immediately upstream of the inlet 148 of a tubular combustion liner 150. As in the first embodiment, the tubular liner 150 is located in spaced relationship radiallyinwardly of the inner surface of the outer casing 106 to form an annular axial recirculation passage 152 therebetween having an inlet 154 in communication with the premix chamber 146 and an outlet 156 therefrom leading to an annular curvilinear passage 158 formed by a curved surface 160 of the outer casing 106 between the outer diameter thereof and the outlet tube 108 thereof.

As in the first embodiment, the liner 150 is supported within the outer casing 106 by six equally spaced circumferential ducts 162 each having an opened inlet 164 connected to the outer casing at an opening 166 therein. An opposite open end 168 is connected to the inner liner 150 at an opening 170 therein to define a flow path for primary air into a plenum space 172 formed between the combustion chamber liner 150 and an inner deflector plate 174.

The inner deflector plate 174 includes a cup-shaped segment 176 with an opened end thereon sealed with respect to the downstream end of the liner 150 by an inner body plug member 178 to close one end of the plenum space 172. The deflector plate 174 further includes an entrance transition section l80 having a plurality of staggered surfaces 182, 184, 186, 188 thereon. Surface 182 has a maximum diameter at 190 that is the entrance to the transition section 180. Each of the surfaces 182 thru 188 are formed angularly with respect to the adjacent surface to form an inwardly converging surface from the maximum diameter 190 to a restricted diameter portion 192 of the deflector plate 174 located between the transition section 180 thereof and the cupshaped outlet segment 176 of deflector plate 174.

As in the first embodiment, the transition section 180 is located immediately downstream of an annular Coanda effect nozzle lip 194 that has one edge 196 thereon connected to the upstream end of the combustion chamber liner 150 and includes a curved surface 198 thereon cooperating with the curved dome to form a curvilinear path from the prevaporizing mix chamber 146 into the inlet 148 of the liner. This leads axially into a primary combustion zone 200 within the deflector plate 174. The lip 194 has an edge 202 thereon spaced closely adjacent the maximum diameter 190 of the transition section 180 to form a gap 204 therebetween which directs primary air received from the ducts 162 as an annular jet across the transition surface 180 to form a wall adhering jet stream from the maximum diameter 198 to the reduced diameter 192.

As in the first embodiment, during the combustion process, primary air and fuel are directed into the swirler assembly which has a tangential component formed at the outlet end 128 of the tube 114. The premixed fuel and vapor components are directed through the gap of the premix chamber 146 to the inlet 148 of the combustion liner 150 as a swirl pattern through the combustion chamber where it is heated and the combustion gases in part are returned in a reverse, external recirculation fiow through the curved passage 158 and the annular passage 152 back to the premix chamber 146 where the gases will heat the tube 114 and the mixed air-fuel components passing through the gap of the chamber 146 so as to prevaporize fuel particles prior to passage into the combustion zone 200.

As was the case in the first embodiment, recirculation passes through a 180 path from the annular passage 152 to the inlet 148 and the pumping action of the jet produced by the gap 204 will reduce pressure losses at this point in the recirculation flow so as to increase the rate of recirculation in the device to improve prevaporization of fuel particles prior to passage into the combustion zone 200.

Furthermore, the jet pumping action through the gap 204 will form a cool envelope around the swirl pattern confining the high velocity portions of the recirculation flow path to the internal walls of the combustion chamber thereby to reduce viscous losses as compared to pure swirl type recirculating systems. As in the first embodiment, the jet flow from the gap 204 flows into a region of decreasing available area normal to flow to result in a reduced tendency for jet separation or reversal of the direction of the entrained flow velocity.

The jet induced recirculation in the embodiment of FIGS. thru 7 is across the inner surface of the deflector plate 174 thence the curved passage 158 back through the annular passage 152 and thence to the inlet 148. This will heat premix components in the chamber 146 to imrpove the combustion process in the chamber 200.

In this embodiment of the invention secondary air openings 206 are located adjacent the transition between the outlet tube 108 and the curved surface 160 of the outer casing 106 to produce further combustion of the fuel-air componentsprior to discharge from the system.

In the first embodiment the recirculation pattern is characterized by an external recirculation fiow produced by the swirl pattern through the annular passage 42. Additionally, there is an internal recirculation pattern produced by jet flow from the gap 100. Addition of an attached jet pumping system in the outer recirculation loop would augment recirculation in the chamber 42 in the same way that the addition of an internal pump augments recirculation of the inner loop.

The basic purpose of the aforedescribed invention is that there is included a unique combination of two methods of producing recirculation; namely, jet pumping and blade induced swirl. The combination yields unique combustor performance advantages over more conventional approaches that include recirculation dependent upon one of the effects alone.

In the embodiment of FIG. I, which is representative of the present invention, the combustor assembly 10 has the following mechanical characteristics.

Item Specification Combustion chamber liner Diffuser section 62 -Continued Item Specification 4 inches outlet diameter Nozzle lip 76 6.875 inches diameter Nozzle gap I00 .190 inches Plate 22 9.895 inches ID.

52 peripheral grooves Groove 92 Width .092 inches 'a mixing chamber upstream of the inlet end of said primary combustion zone, means on the inlet end of said outer casing for producing a swirl pattern within said mixing chamber directed through said annular passage and said primary combustion zone to direct hot gases therefrom into said mixing chamber for prevaporization of air-fuel mixture therein, means including said liner defining a plenum within said outer casing, means for directing primary air from exteriorly of said outer casing into said plenum, an annular nozzle lip supported on said liner in spaced relationship to said deflector plate to define an annular gap therebetween for passage of primary air from said plenum into said combustion zone for directing a quantity of primary air across the inner surface of said inner deflection surface to improve the recirculation flow of hot gases from said primary combustion zone into said mixing chamber thereby to reduce overall pressure drop from the inlet end to the outlet end of said outer casing.

2. A combustor assembly comprising an outer casing having an inlet and an outlet end thereon, a tubular combustion chamber liner located within said outer casing and being spaced therewith to form a radially outer annular recirculation passage between inlet and outlet ends of said outer casing, means forming a primary combustion chamber within said liner having a inlet end and an outlet end thereto, means forming a mixing chamber upstream of said combustion chamber, means including first pump means at the upstream end of said combustion chamber for producing a swirl pattern within said mixing chamber to promote entrainment of air and fuel therein, said swirl pattern producing a reverse axial recirculation of flow from said combustion chamber through said passage into said mixing chamber for increasing the temperature of air-fuel particles therein, means including said liner defining a plenum within said outer casing in surrounding relationship to the combustion chamber, means for directing primary air from exteriorly of said outer easing into said plenum, means including an annular nozzle lip supported on one end of said liner to define an annular gap communicating said plenum chamber with said combustion chamber at one end of said liner for directing a second quantity of primary air through said combustion chamber to enhance said swirl induced reverse recirculation of gases from said combustion chamber into said mixing chamber and to further promote a 180 reversal of flow from said annular chamber at said one end of said liner into said combustion chamber to reduce pressure losses from the inlet end to the outlet end of said outer casing due to recirculation produced by said swirl pattern. v

3. A fuel combustor assembly comprising an outer casing having an inlet end and an outlet end, means forming a mixing chamber downstream of said inlet end, a combustion liner located within said outer casing defining a primary combustion zone therein downstream of said mixing chamber, swirl means for directing a first portion of primary air in a swirl pattern from the inlet end of said casing into said mixing chamber, fuel supply means at said inlet end for directing fuel into said swirl pattern to premix air and fuel within said mixing chamber upstream of said primary combustion zone, an inner deflection plate located radially inward of said combustion liner including a radially outwardly flared inlet end thereon and a converging surface defining a diffusion section, said plate including a radially diverging section at the opposite end of said combustion liner to define a decreasing cross sectional flow area from the outlet end of the combustion liner in the direction of the diffusion section therein, an-annular passage formed between said combustion liner and said outer casing communicating said mixing chamber with the outlet end of said outer casing, said swirl means producing a flow pattern in said annular passage from the inlet end to the outlet end of said outer casing and a resultant reverse axial recirculation of flow through the diverging section of said inner deflection plate and the diffusion section thereon, said swirl means serving to promote flow from said diffusion section through 180 into said annular passage at one end of said combustion liner, and second pump means at the opposite end of said combustion liner for promoting a reverse 180 flow from said annular passage into the diverging section of said inner deflection surface to promote flow of recirculation through the primary combustion zone during combustor operation while reducing overall pressure drop between the inlet and the outlet ends of said combustor casing.

4. A combustor assembly comprising an outer casing having an inlet end and an outlet end, a swirl plate closing the inlet end of said outer casing including a plurality of peripheral grooves therein inclined at an angle with respect to the axis of said outer casing, a mixing chamber in said casing, a fuel supply nozzle supported centrally of said plate directed interiorly of said outer casing, a combustion chamber liner supported within said outer casing in spaced relationship therewith to define an annular passage located concentrically fo said plurality of swirl plate' grooves, an inner deflection plate supported on said combustion liner including an upstream radially outwardly diverging section thereon forming a diffusion section to a primary combustion zone therein, said fuel nozzle having its outlet tip thereon located within said diffusion section, said inner deflection plate including diverging section thereon defining the outlet end of said combustion zone downstream of said diffusion section, a jet nozzle lip secured to said liner forming a circumferential gap facing upstream of said combustion zone at a point downstream of said diverging section, said swirl plate grooves producing a swirl pattern in said mixing chamber upstream of said diffusion section directed into said annular passage and toward the outlet for producing a reverse axial recirculation from the outlet end of said combustion chamber to the inlet end thereof, means for directing primary air through said gap for producing attached wall entrainment of primary air across the diverging section of said deflection plate for promoting recirculation flow through the primary combustion zone, said flow of primary air through said gap promoting reversal of swirl induced flow through said annular passage into the outlet end of said combustion chamber, said swirl plate grooves promoting reversal of axial recirculation outwardly of said diffusion section in a reverse direction through said annular passage thereby to reduce overall pressure drop between the inlet end and the outlet end of said outer casing due to recirculation of flow through said primary combustion zone for producing improved prevaporization of air-fuel mixture within said mixing chamber.

5. A combustor assembly comprising an outer casing .having an inlet end and an outlet end, a combustion liner supported within said outer casing between the opposite ends thereof and defining therewith an annular passage located radially outwardly of said combustion liner between the'inlet and outlet ends of said outer casing, swirl means supported on the inlet end of i said outer casing including an outer tube and a center body portion having a decreasing diameter outer surface configuration, a large diameter end of said center body being located adjacent one end of said outer tube and forming an annular space therebetween, a plurality of swirler vanes supported on the large diameter end of said center body portion each inclined with respect to the longitudinal axis of said outer tube for promoting a swirl pattern from the inlet end of said outer tube to the outlet end thereof, means directing fuel into said outer tube immediately downstream of said swirler vanes to mix air and fuel upstream of said combustion liner, means forming a mixing chamber downstream of said outer tube outlet, an inner deflection plate supported on said combustion liner forming a primary combustion zone within said liner including an inlet end and an outlet end, said swirler vanes producing a swirl pattern through said primary combustion zone from the inlet end to the outlet end thereof and a reverse axial recirculation of flow through said annular passage back to the mixing chamber upstream of said primary combustion zone, said inner deflection plate having a surface diverging inwardly from the mixing chamber to the inlet of said primary combustion zone immediately downstream of said mixing chamber, a nozzle lip located radially outwardly of said inwardly diverging inner surface forming an annular nozzle gap, means for directing primary air into said nozzle gap to produce an attached wall jet of primary air across said inwardly diverging surface for promoting reverse flow of recirculation through said annular passage into the mixing chamber upstream of the inlet to said primary combustion chamber and to enhance the rate of recirculation of flow from the combustion chamber back to the mixing chamber thereby to improve prevaporization of air-fuel particles in said mixing zone prior to passage into said combustion chamber and to reduce pressure drop from the inlet end to the outlet end of said outer casing. 

1. A combustor assembly comprising an outer casing having an inlet and an outlet therein, a combustion liner located within said outer casing and spaced with respect thereto to form an annular external recirculation passage therebetween, means including an inner deflection surface within said combustion chamber liner for forming a primary combustion zone therein having an inlet end and an outlet end, means forming a mixing chamber upstream of the inlet end of said primary combustion zone, means on the inlet end of said outer casing for producing a swirl pattern within said mixing chamber directed through said annular passage and said primary combustion zone to direct hot gases therefrom into said mixing chamber for prevaporization of air-fuel mixture therein, means including said liner defining a plenum within said outer casing, means for directing primary air from exteriorly of said outer casing into said plenum, an annular nozzle lip supported on said liner in spaced relationship to said deflector plate to define an annular gap therebetween for passage of primary air from said plenum into said combustion zone for directing a quantity of primary air across the inner surface of said inner deflection surface to improve the recirculation flow of hot gases from said primary combustion zone into said mixing chamber thereby to reduce overall pressure drop from the inlet end to the outlet end of said outer casing.
 2. A combustor assembly comprising an outer casing having an inlet and an outlet end thereon, a tubular combustion chamber liner located within said outer casing and being spaced therewith to form a radially outer annular recirculation passage between inlet and outlet ends of said outer casing, means forming a primary combustion chamber within said liner having a inlet end and an outlet end thereto, means forming a mixing chamber upstream of said combustion chamber, means including first pump means at the upstream end of said combustion chamber for producing a swirl pattern within said mixing chamber to promote entrainment of air and fuel therein, said swirl pattern producing a reverse axial recirculation of flow from said combustion chamber through said passage into said mixing chamber for increasing the temperature of air-fuel particles therein, means including said liner defining a plenum within said outer casing in surrounding relationship to the combustion chamber, means for directing primary air from exteriorly of said outer casing into said plenum, means including an annular nozzle lip suPported on one end of said liner to define an annular gap communicating said plenum chamber with said combustion chamber at one end of said liner for directing a second quantity of primary air through said combustion chamber to enhance said swirl induced reverse recirculation of gases from said combustion chamber into said mixing chamber and to further promote a 180* reversal of flow from said annular chamber at said one end of said liner into said combustion chamber to reduce pressure losses from the inlet end to the outlet end of said outer casing due to recirculation produced by said swirl pattern.
 3. A fuel combustor assembly comprising an outer casing having an inlet end and an outlet end, means forming a mixing chamber downstream of said inlet end, a combustion liner located within said outer casing defining a primary combustion zone therein downstream of said mixing chamber, swirl means for directing a first portion of primary air in a swirl pattern from the inlet end of said casing into said mixing chamber, fuel supply means at said inlet end for directing fuel into said swirl pattern to premix air and fuel within said mixing chamber upstream of said primary combustion zone, an inner deflection plate located radially inward of said combustion liner including a radially outwardly flared inlet end thereon and a converging surface defining a diffusion section, said plate including a radially diverging section at the opposite end of said combustion liner to define a decreasing cross sectional flow area from the outlet end of the combustion liner in the direction of the diffusion section therein, an annular passage formed between said combustion liner and said outer casing communicating said mixing chamber with the outlet end of said outer casing, said swirl means producing a flow pattern in said annular passage from the inlet end to the outlet end of said outer casing and a resultant reverse axial recirculation of flow through the diverging section of said inner deflection plate and the diffusion section thereon, said swirl means serving to promote flow from said diffusion section through 180* into said annular passage at one end of said combustion liner, and second pump means at the opposite end of said combustion liner for promoting a reverse 180* flow from said annular passage into the diverging section of said inner deflection surface to promote flow of recirculation through the primary combustion zone during combustor operation while reducing overall pressure drop between the inlet and the outlet ends of said combustor casing.
 4. A combustor assembly comprising an outer casing having an inlet end and an outlet end, a swirl plate closing the inlet end of said outer casing including a plurality of peripheral grooves therein inclined at an angle with respect to the axis of said outer casing, a mixing chamber in said casing, a fuel supply nozzle supported centrally of said plate directed interiorly of said outer casing, a combustion chamber liner supported within said outer casing in spaced relationship therewith to define an annular passage located concentrically fo said plurality of swirl plate grooves, an inner deflection plate supported on said combustion liner including an upstream radially outwardly diverging section thereon forming a diffusion section to a primary combustion zone therein, said fuel nozzle having its outlet tip thereon located within said diffusion section, said inner deflection plate including diverging section thereon defining the outlet end of said combustion zone downstream of said diffusion section, a jet nozzle lip secured to said liner forming a circumferential gap facing upstream of said combustion zone at a point downstream of said diverging section, said swirl plate grooves producing a swirl pattern in said mixing chamber upstream of said diffusion section directed into said annular passage and toward the outlet for producing a reverse axial recirculation from the outlet end of said combustion chamber to tHe inlet end thereof, means for directing primary air through said gap for producing attached wall entrainment of primary air across the diverging section of said deflection plate for promoting recirculation flow through the primary combustion zone, said flow of primary air through said gap promoting reversal of swirl induced flow through said annular passage into the outlet end of said combustion chamber, said swirl plate grooves promoting reversal of axial recirculation outwardly of said diffusion section in a reverse direction through said annular passage thereby to reduce overall pressure drop between the inlet end and the outlet end of said outer casing due to recirculation of flow through said primary combustion zone for producing improved prevaporization of air-fuel mixture within said mixing chamber.
 5. A combustor assembly comprising an outer casing having an inlet end and an outlet end, a combustion liner supported within said outer casing between the opposite ends thereof and defining therewith an annular passage located radially outwardly of said combustion liner between the inlet and outlet ends of said outer casing, swirl means supported on the inlet end of said outer casing including an outer tube and a center body portion having a decreasing diameter outer surface configuration, a large diameter end of said center body being located adjacent one end of said outer tube and forming an annular space therebetween, a plurality of swirler vanes supported on the large diameter end of said center body portion each inclined with respect to the longitudinal axis of said outer tube for promoting a swirl pattern from the inlet end of said outer tube to the outlet end thereof, means directing fuel into said outer tube immediately downstream of said swirler vanes to mix air and fuel upstream of said combustion liner, means forming a mixing chamber downstream of said outer tube outlet, an inner deflection plate supported on said combustion liner forming a primary combustion zone within said liner including an inlet end and an outlet end, said swirler vanes producing a swirl pattern through said primary combustion zone from the inlet end to the outlet end thereof and a reverse axial recirculation of flow through said annular passage back to the mixing chamber upstream of said primary combustion zone, said inner deflection plate having a surface diverging inwardly from the mixing chamber to the inlet of said primary combustion zone immediately downstream of said mixing chamber, a nozzle lip located radially outwardly of said inwardly diverging inner surface forming an annular nozzle gap, means for directing primary air into said nozzle gap to produce an attached wall jet of primary air across said inwardly diverging surface for promoting reverse flow of recirculation through said annular passage into the mixing chamber upstream of the inlet to said primary combustion chamber and to enhance the rate of recirculation of flow from the combustion chamber back to the mixing chamber thereby to improve prevaporization of air-fuel particles in said mixing zone prior to passage into said combustion chamber and to reduce pressure drop from the inlet end to the outlet end of said outer casing. 